Hi Skills.. The cheapest method would be to get yourself a membership of your local library, and then see what they have relating to PPL exams and Flight and Navigation etc. If they don't have the required books (i.e. any of the 7 'The Air Pilot's Manuals' by Peter D Goodwin.) then ask them for an Inter-Library Loan, and the books will arrive for you in a week or so.
Ultimately you will get a similar set of these books from your flight school as part of your PPL course, along with some navigational tools.
For general interest you could Google Nats AIP, and wade your way through some of the parts that interest you. Also a trip to your local GA airfield might be useful. When I did that many years ago, they gave me an old 1:500,000 chart for my interest.
If you have an air-band scanner, try to find the frequencies of all the stations within range, and get to understand the 'lingo'. I used to follow a freight airplane from Liverpool to London at 23:30 every night, I got to know which frequency he would switch to next, and could hear him all the way until London at 3000ft.. That was 'Gem-Stone 05 Mike', now no longer flying that route.